Stator cores of electric generators generally have stator windings looped through axially aligned slots in axially adjacent sections of laminations or punchings of electrical steel with radially extending ventilation slots between adjacent core sections for circulating a coolant gas through the stator. The stator cores are generally assembled by pressing core sections together between two core support plates, tensioning several through-bolts extending between the core support plates to tightly clamp the stator core sections and then looping the windings through the axially aligned slots in the core sections. The clamping tightness is checked and rechecked many times during each step of the assembly process and the through bolts are repeatedly tightened, loosened and then retightened. If the core sections are not tightly clamped in the stator, the core sections will vibrate when the generator is operating, which will result in electrical noise and possible physical damage to the insulative coatings on the steel sheets. The sheets may also be subject to contact corrosion. If the sections are clamped together too tightly, the lacquer films applied to stator core sections may be crushed.
As discussed by M. I. Zundelevich and S.A. Prutkovskii in their work "Technology of Heavy Electric Machine Building - Hydrogenerators", clamping tightness is routinely determined by a knife test. In such a test, a shop floor worker manually inserts a tapered side of a knife into a ventilation passage extending between adjacent stator core sections. Zundelevich et al. illustrates a knife having a tapered face about 40 millimeters long which is inserted into a passage up to a depth of about 2 millimeters. The worker then makes a judgment whether the core sections are properly tightened based upon the felt resistance to the penetration of the knife. Thus the test itself is highly subjective and not infrequently results in unnecessary repetitions of the assembly substeps. In addition, the knife test is effected by the condition of the surface of the core sections and the frictional resistance presented to the knife in addition to clamping tightness. Furthermore, the knife may damage the laminations of the adjacent core sections if the knife is not carefully inserted.
Zundelevich et al. describe a pneumatic knife which improves the reliability of knife tests. In the described test, an air cylinder at a predetermined pressure operates a plunger which urges the edge of a knife against an adjacent core section. The worker then merely reads a scale indicating the plunger travel to determine clamping tightness. Although more reliable readings are consistently made with such a pneumatic knife, the test may still be affected by the surface condition of the lamination adjacent the edge of the knife.
It is therefore an object of the present invention to provide a gauge for more reliably determining the clamping tightness of compressed sections.
It is a further object of the invention to provide a clamping tightness gauge which determines the tightness of stator core sections independently of the condition of their surfaces.